Solvent effect on the photogeneration of singlet molecular oxygen by copper tetra(tert-butyl)phthalocyanine

The photogeneration of the singlet molecular oxygen (¹O₂) by copper tetra(4-tert-butyl) phthalocyanine in organic solvents of different nature was substantiated. The apparent quantum yields of ¹O₂in benzene and pyridine were determined. The data obtained indicate an influence of the coordinating properties of the solvent on the ¹O₂yield. However, this factor is not “critical” as in the case of photogeneration of ¹O₂by copper tetra(5-tert-butylpyrazino)porphyrazine.     

Kinetics and mechanism of the highly efficient generation of singlet oxygen in dimethyldioxirane decomposition induced by the chloride ion

The decomposition of dimethyldioxirane induced by the chloride anion has been investigated by methods of infrared chemiluminescence and quantum chemistry. The reaction leads to efficient generation of singlet excited molecular oxygen ¹O₂ (the excitation yield in acetone is 61%). A mechanism of peroxide decomposition is proposed in which the key reactions are the addition of the chloride ion to an oxygen atom of dioxirane, resulting in dioxirane ring opening and the formation of the 2-chlorooxy-2-hydroxy propane alcoholate (k ₁), and the interaction of the latter with another dimethyldioxirane molecule. This interaction results either in the formation of an adduct, which further decomposes to evolve ¹O₂, and catalyst regeneration (k ₂) or in the formation of the 2-chloroxyisopropyl radical, which leads to the irreversible consumption of the chloride ion catalyst (k ₃). The decay kinetics of the infrared chemiluminescence of ¹O₂ has been studied in a wide range of reactant concentrations. The temperature dependence of the rate constant of the reaction of dimethyldioxirane with the chloride ion has been determined by a kinetic analysis of the mechanism proposed: log(² k ₁) = (11.1 ± 0.7) − (46 ± 4)/Θ, where Θ = 2.3RT kJ/mol. Estimation of the ratio of the rates of the reaction of the 2-chlorooxy-2-hydroxy propane alcoholate with dimethyldioxirane via two pathways (k ₃/k ₂) has demonstrated that the fraction of the process involving electron transfer does not exceed 1.5% under the experimental conditions examined. Nevertheless, the latter reaction, which withdraws the chloride ion from the catalytic cycle of dimethyldioxirane decomposition yielding singlet oxygen, has a marked effect on the overall kinetics of the process.     

Vacancy Contents in MnZn Ferrites From TG Curves

Expressions for calculating the cation vacancy contents of MnZn ferrites from thermogravimetric curves are presented together with some experimental data. In a single-phase MnZn ferrite synthesized by conventional ceramic procedures, the O₂ evolution accompanying ferrite formation follows the formal equation. Mn²⁺ _σα Zn_σβ Fe³⁺ _2σ(1–γ) [V ]_{σ/4(1–2γ)} O₄ =σ'/σ Mn²⁺ _σ(α–2ϕ) Zn_σβ Fe²⁺ _2σθ Mn³⁺ _2σϕ Fe³⁺ _{2σ(1–γ–θ)} [V ]_{σ/4(1–2γ–3ϕ)} O₄ +σ'φ/2O₂ (g) where α and β denote the MnO and ZnO mole fractions in the primary mixture γ=α+β, θ and ϕ depend on the quantities of Fe²⁺ and Mn³⁺ formed, respectively, φ=θ–ϕ and σ'/σ is a function of the former parameters. Even though the relative amounts of Fe²⁺ /Fe³⁺ and Mn²⁺ /Mn³⁺ remain uncertain, the vacancy content [V ] of the ferrite can be determined because it depends on φ alone, which is related to the change in mass of the sample as the synthesis takes place through the equation φ=(1.5–γ) μ_β /μ_O2 (1–m _f /m _i ) Here, m _i and m _f are the masses of the sample before and after O₂ evolution, μ_B is the formula mass of the ferrite and μ_O2 is the O₂ molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250°C and cooling in pure N₂ . This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of the quantum yield of singlet oxygen sensitized by halogenated boron difluoride dipyrromethenes

The spectral–luminescent, photophysical, and photochemical properties of dichloro-, dibromo-, and diiodo-derivatives of boron dipyrromethenate (BODIPY) have been studied, as well as the feasibility of generating singlet oxygen (¹O₂) via its photosensitization by the dihalogenated derivatives of BF₂ dipyrromethene in solutions. Quantum yields of singlet oxygen have been determined using 1,3-diphenylisobenzofuran as the ¹O₂ trap. The lowest fluorescence quantum yields have been shown to correspond to the maximum yields of singlet oxygen. It has been found that the best ¹O₂ photosensitizer among the three test dihalotetraphenylaza- BODIPY is dibromotetraphenylaza-BODIPY, which in addition possesses the highest photostability. Diiodotetramethyl-BODIPY results in the singlet oxygen yield close to unity, but it has significantly lower photostability. The yield of singlet oxygen is affected by the solvent. Dibromtetraphenylaza-BODIPY and diiodotetramethyl-BODIPY may find use as a medium in photodynamic therapy and photocatalysis of oxidation reactions.     

Free radical/singlet dioxygen system under the conditions of catalytic hydrogen peroxide decomposition

Hydrogen peroxide decomposition and the oxidation of unsaturated compounds (anthracenes, alkenes, etc.) in the H₂O₂/V^(V)/AcOH system occur via a molecular mechanism. H₂O₂ decomposes to yield singlet dioxygen¹O₂(¹Δ_g). Among V^V peroxo complexes of different compositions, coordinated Superoxide radical anions V^(V)(O2/∸) are found in a steady-state concentration in the system under investigation. Styrene oxidation in the H₂O₂V^(V)/AcOH system unusually accelerates in the presence of 2,6-di-tert-butyl-4-methylphenol (BHT), which is an inhibitor of radical chain reactions. This is explained by a decrease in the V^(V)(O ₂ ^∸ ) concentration and an increase in the concentration of dissolved¹O₂ in the presence of ionol. A new phenomenon in the chemistry of singlet dioxygen is found: the ESR signal from the paramagnetic system upon its interaction with¹O₂ broadens in an unusually drastic manner (up to 10 G). This broadening is virtually independent of the nature of the radicals, the acidity of the medium, and the nature of the metal catalysts used for the generation of¹O₂(¹Δ_g).     

Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1Δg)) Production by 9H‐Fluoren‐9‐one: Solvents and Solvent Mixtures

We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O₂(¹Δ_g), denoted as ¹O₂) by 9H‐fluoren‐9‐one (FLU). The normalized empirical parameter E derived from E_T(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of ¹O₂ production (Φ_Δ) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (Φ_ISC). Values of Φ_Δ of unity have been found in alkanes. In nonprotic solvents of increasing polarity, Φ_ISC and, therefore, Φ_Δ decrease due to solvent‐induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor ¹O₂ sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing Φ_Δ to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of Φ_Δ upon addition of increasing amounts of the latter.     

Osmotic Coefficients of the Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>+LiCl + H<Subscript>2</Subscript>O System at <Emphasis Type="Italic">T</Emphasis>=273.15 K

Osmotic coefficients and water activities for the Li₂B₄O₇+LiCl+H₂O system have been measured at T=273.15 K by the isopiestic method, using an improved apparatus. Two types of osmotic coefficients, φ _S and φ _E, were determined. φ _S is based on the stoichiometric molalities of the solute Li₂B₄O₇(aq), and φ _E is based on equilibrium molalities from consideration of the equilibrium speciation into H₃BO₃,B(OH)₄⁻ and B₃O₃(OH)₄⁻. The stoichiometric equilibrium constants K _m for the aqueous speciation reactions were estimated. Two types of representations of the osmotic coefficients for the Li₂B₄O₇+LiCl+H₂O system are presented with ion-interaction models based on Pitzer’s equations with minor modifications: model (I) represents the φ _S data with six parameters based on considering the ion-interactions between three ionic species of Li⁺, Cl⁻, and B₄O₇²⁻, and model (II) for represents the φ _E data based on considering the equilibrium speciation. The parameters of models (I) and (II) are presented. The standard deviations for the two models are 0.0152 and 0.0298, respectively. Model (I) was more satisfactory than model (II) for representing the isopiestic data.     

Syntheses and characterization of three hybrid materials based on polymeric copper complexes and saturated Keggin polyoxoanions

Three novel heteropolytungstates, [Cu(phen)₂]₄[α-SiW₁₂O₄₀] (1), [Cu₄(4,4′-bpy)₃(2,2′-bpy)₄][α-SiW₁₂O₄₀] · H₂O (2) and [Cu(4,4′-bpy)(4,4′-Hbpy)_0.5]₂[PW₁₂O₄₀] (3) (phen = 1,10-phenanthroline, 4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine), have been synthesized and characterized by elemental analyses, IR, TG analyses and single-crystal X-ray diffraction. Compound (1) exhibits interesting chiral layer constructed from interperpendicular helical chains running along a crystallographic 2₁ axis in the c and a directions. Furthermore, the chiral layers are connected by the [α-SiW₁₂O₄₀]⁴⁻ anions via hydrogen bonding interactions to form a 3D superamolecular structure. The [Cu₄(4,4′-bpy)₃(2,2′-bpy)₄]⁴⁺ coordinated complexes in compound (2) are packed together via the aromatic π–π stacking interactions and exhibit an interesting 3D sandglasslike “host” network with 1D channels, in which [α-SiW₁₂O₄₀]⁴⁻ anions “guests” reside. Compound (3) has a unique 2D superamolecular network, which is composed of cationic Cu^I coordination polymer chains and discrete [PW₁₂O₄₀]³⁻ polyoxoanions as linkers. It is noteworthy that the monprotonated 4,4′-bpy ligands of (3) act as arms and connect the adjacent 2D network, generating a 3D interpenetrating superamolecular structure.     

Isopiestic Determination of the Osmotic Coefficients and Pitzer Model Representation for the Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>+LiCl + H<Subscript>2</Subscript>O System at <Emphasis Type="Italic">T</Emphasis>=298.15 K

Isopiestic molalities and water activities have been measured for the Li₂B₄O₇+LiCl + H₂O system at T=298.15 K using an improved isopiestic apparatus. Two types of osmotic coefficients, φ _S and φ _E, were determined, where φ _S is based on the stoichiometric molalities of the solute Li₂B₄O₇(aq) and φ _E is based on equilibrium molalities calculated by consideration of the equilibrium speciation of Li₂B₄O₇ to partially form H₃BO₃, B(OH)₄⁻ and B₃O₃(OH)₄⁻. The stoichiometric equilibrium constant K _m for the aqueous speciation reaction was estimated. Two representations of the osmotic coefficients of Li₂B₄O₇ + LiCl + H₂O were made with Pitzer’s ion-interaction model. Model (1) involved representing the φ _S values with six parameters based on considering the ionic interactions between Li⁺, Cl⁻, and B₄O₇²⁻; and model (2) involved representing the φ _E values based on the calculated equilibrium speciation. Reasonable agreements were obtained between the experimental osmotic coefficient data and those calculated using the above models, with standard deviations of 0.075 and 0.0229, respectively, for these two models. The thermodynamic osmotic coefficients for the complex system containing polymeric boron anions and lithium cation was modelled and explained by use of Pitzer’s ion-interaction model, with minor modifications in combination with speciation reaction equilibria.     

Theoretical studies of electron and hydrogen transfer reactions between semiquinone radicals and oxygen

 To explore the interactions between ubiquinones and oxygen in living organisms, the thermodynamics of a series of electron and hydrogen transfer reactions between semiquinone radicals, as well as their corresponding protonated forms, and oxygen, singlet or triplet, were studied using the hybrid Hartree–Fock–density functional theory method Becke's three parameter hybrid method with the Lee, Yang, and Parr correlation functional. Effects of the solvent and of the isoprenyl tail on the electron and hydrogen transfer reactions were also investigated. It is found that semiquinone radicals (semiquinone anion radicals or protonated semiquinone radicals) cannot react with triplet oxygen to form the superoxide anion radical O₂ ⁻. In contrast, neutral quinones can scavenge O₂ ⁻ efficiently. In the gas phase, only protonated semiquinone radicals can react spontaneously with singlet oxygen to produce peroxyl radical (HO₂). However, both semiquinone anion radicals and protonated semiquinone radicals can react with singlet oxygen to produce harmful oxygen radicals (O₂ ^{− a l l b u l l} and HO₂, respectively) in aqueous and protein environments. The free-energy changes of the corresponding reactions obtained for different ubiquinone systems are very similar. It clearly shows that the isoprenyl tail does not influence the electron and hydrogen transfer reactions between semiquinone radicals and oxygen significantly. Results of electron affinities, vertical ionization potentials, and proton affinities also show that the isoprenyl tail has no substantial effect on the electronic properties of ubiquinones. Received: 3 July 2000 / Accepted: 6 September 2000 / Published online: 21 December 2000     

Room-Temperature Near-Infrared Metastable Species Measured by Phase-Sensitive Lock-in and Fourier Transform Techniques

An ultrasensitive detecting system coupled with either a lock-in or Fourier transform technique has been used to detect near-infrared (1000-2500 nm) metastable species in room temperature solutions. These species include O₂(¹Δ_g), O₂(¹σ⁺_g), the solvent induced satellite peak of molecular singlet oxygen (¹Δ_g) emission, and the triplet state of bis(triisobutylsiloxy)silicon-2,-3-naphthalocyanine (SilNC). Using the O₂(¹Δ_g) emission in benzene as a standard, the quantum yield and radiative decay rate of SiINC triplet state have been determined. Depending on types of spectral acquisition, special techniques such as phase-distinguishing and step scan capabilities were utilized. Their advantages and disadvantages are discussed.     

Structural characterization of two lanthanide complexes attached to [H<Subscript>2</Subscript>W<Subscript>12</Subscript>O<Subscript>40</Subscript>]<Superscript>6−</Superscript>

In this article, two compounds [H₂bpy][Ln(DMF)₄(H₂O)₃(Hbpy)][H₂W₁₂O₄₀] (Ln = La,Ce; DMF = N,N-dimethylformamide, bpy = 4,4′-bipyridine) have been synthesized and characterized by single-crystal X-ray diffraction, IR spectra, and TG analysis. X-Ray analysis showed that the [Ln(DMF)₄(H₂O)₃(Hbpy)]⁴⁺ unit is supported on the α-Keggin polyoxoanion [H₂W₁₂O₄₀]⁶⁻ via the surface bridging oxygen atom. The [H₂bpy][Ln(DMF)₄(H₂O)₃(Hbpy)][H₂W₁₂O₄₀] entity is further extended into 2D supramolecular networks with 1-D channels by hydrogen-bonding interactions, in which 4,4′-bipy ligands reside. To the best of our knowledge, these complexes represent the first examples of rare earth metal-organic complex-decorated α-metatungstate clusters. Furthermore, the electrochemical properties of these compounds have been studied via the method of bulk-modified carbon paste electrodes.     

Multivariate statistical treatment of solvent effects in the photoreduction of CoIII(En)2(Br)(RC6H4NH2)2+ complexes in aqua-organic solvent media

Ultraviolet photolysis (λ = 254 nm) studies were carried out for a series of cobalt(III) complexes, Co^III(En)₂(Br)(RC₆H₄NH₂)²⁺, where R = m-OMe, p-F, H, m-Me, p-Me, p-OEt, and p-OMe, in various compositions of water-methanol/1,4-dioxane mixtures (0, 5, 10, 15, 20, 25, and 30 vol % organic cosolvent) at two different temperatures (287 and 300 K). The ligand-to-metal charge-transfer excited state produced in the excitation of the complex initially generated a solvent-caged {Co^II; ligand radical} pair, which eventually undergoes recombination/separation into products. The quantum yield sharply increased from a mixture containing a lower mole fraction of organic cosolvent (x _org) to higher one. In other words, when x _org in the mixture increases, a steady increase in the quantum yield is observed. The quantum yield of Co^III(En)₂(Br)(RC₆H₄NH₂)²⁺ in various solvent mixtures is found to exhibit a linear (logΦ_Co(II) − 1/ε_r) dependence. This is consistent with solvation or solvent cage effect, which may be nonspecific, specific, or both. In order to throw light on these effects, a phenomenological model of solvent effects was applied. Therefore, the quantum yield values have been correlated statistically with some success containing different solvent parameters. The solvent parameters considered in this work are Grunwald-Winstein’s Y, Krygowski-Fawcett’s E _T ^N and DN ^N along with Kamlet-Taft’s α, β, π* parameters. The regression model proposed is Y _S = Y ₀ + Σ _{i = 1} ⁿ a _i X _i , where Y_S is the solvent-dependent property (here logΦ_Co(II)) in a given solvent; Y ₀ is the statistical quantity corresponding to the value of property in the reference solvent; X ₁, X ₂, X ₃ … are explanatory variables, the solvent parameters, which can explain the various solvation effects on reactants/{Co^II; ligand radical} pair, and a ₁, a ₂, a ₃… etc., are the regression coefficients. The coefficient values can be quantified to measure the relative importance of solvent effects on the physicochemical quantity, that is, the photoreduction yields in the present investigation. The text was submitted by the author in English.     

Mechanism of the O2(1Δg) generation from the Cl2/H2O2 basic aqueous solution explored by the combined ab initio calculation and nonadiabatic dynamics simulation

In the present work, mechanism of the O₂(¹Δ_g) generation from the reaction of the dissolved Cl₂ with H₂O₂ in basic aqueous solution has been explored by the combined ab initio calculation and nonadiabatic dynamics simulation, together with different solvent models. Three possible pathways have been determined for the O₂(¹Δ_g) generation, but two of them are sequentially downhill processes until formation of the OOCl⁻ complex with water, which are of high exothermic character. Once the complex is formed, singlet molecular oxygen is easily generated by its decomposition along the singlet-state pathway. However, triplet molecular oxygen of O₂() can be produced with considerable probability through nonadiabatic intersystem crossing in the ¹Δ_g/ intersection region. It has been found that the coupled solvent, heavy-atom, and nonadiabatic effects have an important influence on the quantum yield of the O₂(¹Δ_g) generation. © 2018 Wiley Periodicals, Inc.     

Immobilization of porphyrins in poly(hydroxymethylsiloxane)

Three tetracationic porphyrins differing in the position of charged nitrogen atoms on the peripheral substituents — 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP4), 5,10,15,20-tetrakis(N-methylpyridinium-2-yl)porphyrin (TMPyP2), 5,10,15,20-tetrakis(4-trimethylammoniophenyl) porphyrin (TMAPP), and hydrophobic 5,10,15,20-tetraphenylporphyrin (TPP), were immobilized by adsorption and encapsulation in poly(hydroxymethylsiloxane) (PHOMS). The so prepared porphyrin-PHOMS composites were characterized by porosimetry, scanning electron microscopy, fluorescence and diffuse reflectance UV-VIS spectroscopy. It was found that porphyrins are immobilized in the PHOMS matrix in the free base monomer form Their irradiation produced singlet oxygen O₂(¹Δ_g) with the lifetime of 10–30 μs.     

Synthesis, structural characterization and properties of a 3D infinitely extended structural rare earth coordination compound of K3{[Sm(H2O)7]2Na[α-SiW11O39Sm(H2O)4]2} · 14 H2O· 14 H2O

A 3D infinitely extended structural rare earth coordination compound with a formula of K₃{[Sm(H₂O)₇]₂Na[α-SiW₁₁O₃₉Sm(H₂O)₄]₂}·14H₂O has been synthesized by reaction of Sm₂O₃, HClO₄, NaOH with α-K₈SiW₁₁O39·nH₂O, and characterized by IR, UV spectra, ICP, TG-DTA, cyclic voltammetry, variable-temperature magnetic susceptibility and X-ray single-crystal diffraction. X-ray single-crystal diffraction indicates that the title compound crystallizes in a triclinic lattice, Pī space group, with a = 1.2462(3) nm, b = 1.2652(3) nm, c = 1.8420(4) nm, α = 87.45(3)°, β = 79.91(3)°, γ= 82.57(3)°, Z = 1, R₁ = 0.0778, wR₂ = 0.1610. Structural analysis reveals that Sm³⁺(1) coordination cation has incorporated into the vacant site of [α-SiW11O₃₉]⁸⁻ entity, forming the [α- SiW₁₁O₃₉Sm(H₂O)₄]⁵⁻ subunit. The two adjacent [α-SiW₁₁O₃9Sm(H₂O)4]⁵⁻ subunits are combined with each other through two Sm(1)-O-W bridges accompanying the formation of dimmer structural unit [α-SiW₁₁O₃₉Sm(H₂O)₄]₂ ¹⁰⁻ of the title compound. The neighboring dimmer structural units [α-SiW₁₁O₃₉Sm(H₂O)₄]₂ ¹⁰⁻ are linked to form the 1D chainlike structure by means of two Sm³⁺(2) and a Na⁺(1) coordination cations. The K⁺(1) cations connect the 1D packing chains constructing the 2D netlike structure, and adjacent netlike layers are also grafted by K⁺(2) cations to build the novel 3D infinitely extended structure. The result of TG-DTA curves manifests that the decomposition temperature of the title polyanionic framework is 554°C. The cyclic voltammetry measurements show that the title polyanion has the two-step redox processes in aqueous solution with pH = 3.1. Variable temperature magnetic susceptibility indicates the title compound obeys the Cruie-Weiss Law in the higher temperature range from 110 to 300 K, while in the lower temperature range from 2 to 110 K the comparatively strong antiferromagnetism interactions can be observed.     

Theoretical treatment of predissociation of the CO (3sσ) B and (3pσ) C1Σ+ Rydberg states based on a rigorous adiabatic representation

Ab initio multireference configuration interaction calculations for adiabatic potential curves, nonadiabatic couplings 〈φ _i (R,r)|d/dR|φ _j (R,r)〉 and 〈φ _i (R,r)|d²/dR ²|φ _j (R,r)〉, and nuclear kinetic energy corrections 〈dφ _i (R,r)/dR|dφ _i (R,r)/dR〉 for the (3sσ) B and (3pσ) C¹Σ⁺ Rydberg states of the CO molecule have been carried out. The energy positions and predissociation linewidths for the observed vibrational levels of these two states have been determined in a rigorous adiabatic representation by the complex scaling method employing a basis of complex scaled harmonic vibrational functions in conjunction with the Gauss-Hermite quadrature method to evaluate the complex Hamiltonian matrix elements. The present treatment correctly reproduces the observed trends in energies and line broadening for vibrational levels of the B¹Σ⁺ state and represents an improvement over the previous treatment in literature. The errors in the determined spacings of the v = 0–4 vibrational levels of the C¹Σ⁺ state are less than 2% compared with measured data. The predissociation linewidths for the v=3,4 levels of the C¹Σ⁺ state are found to be 4.9 and 8.9 cm⁻¹, respectively, in good agreement with the observed values. Received: 23 March 1998 / Accepted: 27 July 1998 / Published online: 9 October 1998     

Photochemical and photophysical study on the kinetics of the atmospheric photodissociation of acetone

The pressure dependence of the photodissociation quantum yield of acetone has been determined in different buffer gases at 308 nm. Results by Stern-Volmer analyses are in accordance with a suggested photolysis mechanism. Luminescence spectra, lifetimes and transition dipole moments have been determined. The energy transfer process by O₂ to give O₂(¹Δ_g) is of minor importance in the case of the singlet excited state of acetone, while it is the dominant deactivation process for the triplet state.     

Solution Stoichiometry Control for Pure LiLaMo2O8Phases in Sol-Gel Preparation

The hydrolysis of solutions, containing either LiMo₂O₄(OPr ⁱ )₅( ⁱ PrOH) and “La(OPr ⁱ )₃” or LiOPr ⁱ and La₂Mo₄O₈(OPr ⁱ )₁₄ in 1∶1 ratio, in toluene or ⁱ PrOH, by water solutions in isopropanol, leads to formation of monolythic gels. The latter can be converted by drying and heat treatment at 600°C into a fine powder of pure α-LiLaMo₂O₈ phase, which is transformed into β-LiLaMo₂O₈ powder by annealing at 800°C. The sintering of the pellets pressed under 4 bar pressure of α-LiLaMo₂O₈ powder at 800°C for 2 h converts them into pieces of β-LiLaMo₂O₈ transparent ceramics, thus providing a route to LiLnMo₂O₈ laser waveguide materials.     

A Dimeric Fe(III)-Substituted α-Keggin Tungstogermanate: {[α-GeFe2W10O38(OH)]2}14−

The dimeric Fe(III)-substituted α-Keggin tungstogermanate {[α-GeFe₂W₁₀O₃₈(OH)]₂}¹⁴⁻ (1) was synthesized by reaction of iron(III) with [A-α-GeW₉O₃₄]¹⁰⁻ in neutral medium and characterized by elemental analysis, IR, UV-Vis, TG-DSC and electrochemistry. An X-ray single-crystal analysis was carried out on K₁₄[α-GeFe₂W₁₀O₃₈(OH)]₂ ·34H₂O, which crystallizes in the monoclinic system, space group P2₁/c, with a = 20.510(3) ?, b = 15.565 (2) ?, c = 17.998(2) ?, β = 114.672(2)° and Z = 2. The polyanion 1 consists of two [α-GeFe₂W₁₀O₃₈(OH)] Keggin moieties linked via two bridging hydroxo groups, leading to a planar Fe₄O₂(OH)₂ cluster. The two half-units are related by an insertion center. The locating of the hydroxo groups is done by the bond valence sum calculations. The TG-DSC results show that the polyanion 1 is stable below 520 °C.